refactor(task,render): RenderTask family over a new oakrender ticket C ABI

- oakrender: new ticket family (render_frame/render_audio with finished
  callback, result frame/samples access, cancel/wait), project copier
  C API, cache get_invalidated_ranges, manager set_aggressive_gc
- oaknode: node_copy_inputs, set_value_hint_track, viewer params
  setters, video frame cache borrowed outlet, project copy_settings
- oakcodec: encoder desired pixel format, export format extension,
  encoding generate_matrix, custom range in encoding params POD
- oaktask: RenderTask orchestrates oakrender tickets (no Qt threads/
  watchers), PreCacheTask and ExportTask rewritten over the oaknode/
  oakrender/oakcodec C ABIs; frames cross from oakrender to oakcodec
  handles by pixel copy (different control blocks)
- the two-step texture/download render path collapses into single-step
  (tickets always yield frames); subtitle sidecar kept
- tests: 105 in build-oaktask (export/precache factory paths,
  construction, conform end-to-end); regressions all green

include/codec/encoder.h

@@ -116,6 +116,14 @@ typedef struct oakcodec_encoding_params {
 
 	int export_length_num; /**< Export length in seconds (rational). */
 	int export_length_den;
+
+	/** Custom export range (seconds, rational pairs); used when
+	 * has_custom_range != 0. */
+	int has_custom_range;
+	int64_t custom_range_in_num;
+	int64_t custom_range_in_den;
+	int64_t custom_range_out_num;
+	int64_t custom_range_out_den;
 } oakcodec_encoding_params;
 
 /**
@@ -185,6 +193,29 @@ OAKCODEC_API int oakcodec_encoder_flush(OakEncoder encoder);
  */
 OAKCODEC_API int oakcodec_encoder_last_error(OakEncoder encoder, char *buf, int buf_size);
 
+/**
+ * @brief The pixel format the encoder wants frames in
+ *        (Encoder::get_desired_pixel_format()), as int; -1 when
+ *        unknown/invalid encoder.
+ */
+OAKCODEC_API int oakcodec_encoder_get_desired_pixel_format(OakEncoder encoder);
+
+/**
+ * @brief File extension for an export format
+ *        (ExportFormat::get_extension()), two-stage string getter.
+ */
+OAKCODEC_API int oakcodec_export_format_get_extension(int format, char *buf,
+									 int buf_size);
+
+/**
+ * @brief Scaling matrix for a scaling method
+ *        (EncodingParams::generate_matrix()), row-major 4x4 into
+ *        out_matrix[16].
+ */
+OAKCODEC_API int oakcodec_encoding_generate_matrix(int method, int src_width,
+								  int src_height, int dst_width,
+								  int dst_height, double *out_matrix);
+
 #ifdef __cplusplus
 }
 #endif

include/node/node.h

@@ -23,6 +23,7 @@
 
 #include <stdint.h>
 
+#include "common/videoparams.h"
 #include "node/error.h"
 #include "undo/undocommand.h"
 
@@ -110,6 +111,16 @@ typedef struct OakNodeProject OakNodeProject;
 typedef struct OakNodeMarkerList OakNodeMarkerList;
 typedef struct OakNodeWorkArea OakNodeWorkArea;
 
+/**
+ * @brief Opaque borrowed handle to a node's video frame cache
+ * (olive::FrameHashCache in oakrender). oakrender reinterprets this into
+ * its own handle types.
+ */
+typedef struct OakNodeFrameCache OakNodeFrameCache;
+
+/* oakcore handles used by the viewer setters. */
+typedef struct OakAudioParams OakAudioParams;
+
 /**
  * @brief Number of live owned objects created through this API
  * (nodes from oaknode_factory_create_from_id()/oaknode_node_create_copy(),
@@ -543,6 +554,40 @@ int oaknode_node_get_markers(const OakNodeNode *node,
 int oaknode_node_get_work_area(const OakNodeNode *node,
 							   OakNodeWorkArea **out);
 
+/**
+ * @brief Borrowed video frame cache of a node (NULL when the node has
+ *        none or for NULL input).
+ */
+int oaknode_node_get_video_frame_cache(const OakNodeNode *node,
+									   OakNodeFrameCache **out);
+
+/**
+ * @brief Copy input values/connections from one node to another
+ *        (Node::copy_inputs()). include_connections != 0 also copies
+ *        input connections.
+ */
+int oaknode_node_copy_inputs(OakNodeNode *dst, const OakNodeNode *src,
+							 int include_connections);
+
+/**
+ * @brief Set a track-routing value hint on an input
+ *        (Node::set_value_hint_for_input() with a single texture type
+ *        and a Track::Reference string).
+ */
+int oaknode_node_set_value_hint_track(OakNodeNode *node,
+									  const char *input_id,
+									  int track_type, int track_index);
+
+/**
+ * @brief Set a viewer node's video/audio params (ViewerOutput::
+ * set_video_params/set_audio_params, stream index 0). `params` is an
+ * oakcommon handle (video) or borrowed oakcore handle (audio).
+ */
+int oaknode_viewer_set_video_params(OakNodeNode *viewer,
+									const OakVideoParams *params);
+int oaknode_viewer_set_audio_params(OakNodeNode *viewer,
+									const OakAudioParams *params);
+
 /**
  * @brief Create a command that removes a node from its graph together
  * with its exclusive dependencies and disconnects its edges

include/node/project.h

@@ -163,6 +163,12 @@ int oaknode_project_is_new(const OakNodeProject *project);
 int oaknode_project_cache_path(const OakNodeProject *project, char *buf,
 							   int buf_size);
 
+/**
+ * @brief Copy all project settings (Project::copy_settings()).
+ */
+int oaknode_project_copy_settings(OakNodeProject *dst,
+								  const OakNodeProject *src);
+
 /**
  * @brief Cache location setting enum value
  * (Project::get_cache_location_setting(): 0 = default location,

include/render/cache.h

@@ -107,6 +107,20 @@ int oakrender_cache_has_validated_ranges(const OakRenderCache *cache);
  */
 int oakrender_cache_indicator_height(void);
 
+/**
+ * @brief The invalidated sub-ranges of [in, out) as flat
+ *        {in_n, in_d, out_n, out_d} quadruples
+ *        (PlaybackCache::get_invalidated_ranges()).
+ *
+ * Two-stage: call with ranges == NULL (or max_ranges == 0) to get the
+ * count; then call with a buffer of max_ranges * 4 int64_t values.
+ *
+ * @return Range count (>= 0), or a negative OAKRENDER_E_* code.
+ */
+int oakrender_cache_get_invalidated_ranges(OakRenderCache *c,
+		int64_t in_num, int64_t in_den, int64_t out_num, int64_t out_den,
+		int64_t *ranges, int max_ranges);
+
 /**
  * @brief Load a cached frame from disk
  * (FrameHashCache::load_cache_frame(cache_path, uuid, ts)).

include/render/copier.h

@@ -0,0 +1,65 @@
+/***
+
+  Oak Video Editor - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef OAK_EDITOR_RENDER_COPIER_H
+#define OAK_EDITOR_RENDER_COPIER_H
+
+#include "node/node.h"
+#include "node/project.h"
+#include "render/error.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Opaque handle to a project copier (olive::ProjectCopier):
+ *        deep-copies a project graph for background processing
+ *        (export/precache).
+ */
+typedef struct OakRenderProjectCopier OakRenderProjectCopier;
+
+/**
+ * @brief Create a copier. The copy is built by
+ *        oakrender_project_copier_set_project().
+ */
+OakRenderProjectCopier *oakrender_project_copier_create(void);
+
+/** @brief Free the copier AND its copied project. NULL-safe. */
+void oakrender_project_copier_free(OakRenderProjectCopier *copier);
+
+/** @brief (Re)build the copy from `project`. */
+int oakrender_project_copier_set_project(OakRenderProjectCopier *copier,
+										 OakNodeProject *project);
+
+/** @brief The copied counterpart of an original node (borrowed), NULL
+ *        when the node is not in the copied project. */
+OakNodeNode *oakrender_project_copier_get_copy(
+	OakRenderProjectCopier *copier, OakNodeNode *original);
+
+/** @brief The copied project (borrowed). */
+OakNodeProject *oakrender_project_copier_get_copied_project(
+	OakRenderProjectCopier *copier);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //OAK_EDITOR_RENDER_COPIER_H

include/render/ticket.h

@@ -0,0 +1,156 @@
+/***
+
+  Oak Video Editor - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef OAK_EDITOR_RENDER_TICKET_H
+#define OAK_EDITOR_RENDER_TICKET_H
+
+#include <stdint.h>
+
+#include "common/colortransform.h"
+#include "common/videoparams.h"
+#include "node/colormanager.h"
+#include "node/node.h"
+#include "olive/core/oakcore/audioparams.h"
+#include "olive/core/oakcore/samplebuffer.h"
+#include "render/error.h"
+#include "render/color.h"
+#include "render/renderer.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Opaque handle to a render ticket (olive::RenderTicketWatcher).
+ *
+ * Created by oakrender_ticket_render_frame() /
+ * oakrender_ticket_render_audio(); free with oakrender_ticket_free().
+ */
+typedef struct OakRenderTicket OakRenderTicket;
+
+/**
+ * @brief Finished callback (async command return channel, 01 §4
+ *        exception). Fires on the ticket's finishing thread, exactly
+ *        once (cancelled tickets fire with a NULL result).
+ */
+typedef void (*oakrender_ticket_finished_fn)(OakRenderTicket *ticket,
+											 void *userdata);
+
+/** @brief Ticket types (RenderManager::TicketType). */
+enum OakRenderTicketType {
+	OAKRENDER_TICKET_VIDEO = 0,
+	OAKRENDER_TICKET_AUDIO = 1
+};
+
+/**
+ * @brief Parameters for a video frame ticket
+ *        (RenderManager::RenderVideoParams).
+ */
+typedef struct oakrender_video_ticket_params {
+	OakNodeNode *output_node; /**< Connected texture output node. */
+	OakVideoParams video_params; /**< By value (oakcommon handle). */
+	OakAudioParams *audio_params; /**< Borrowed oakcore handle, may be NULL. */
+	int64_t time_num; /**< Frame timestamp as rational. */
+	int64_t time_den;
+	OakNodeColorManager *color_manager; /**< Borrowed, may be NULL. */
+	int mode; /**< olive::RenderMode::Mode as int. */
+	int force_width; /**< 0/0 = off. */
+	int force_height;
+	double force_matrix[16]; /**< Used when has_force_matrix != 0. */
+	int has_force_matrix;
+	int force_format; /**< PixelFormat as int, -1 = off. */
+	int force_channel_count; /**< 0 = off. */
+	OakColorProcessor *force_color_output; /**< May be NULL. */
+	OakColorTransform force_color_transform; /**< By value; empty ctx = default. */
+	OakNodeFrameCache *cache; /**< Borrowed frame cache, may be NULL. */
+} oakrender_video_ticket_params;
+
+/**
+ * @brief Submit a video frame render ticket.
+ *
+ * @return Ticket handle (caller frees), or NULL on failure. The finished
+ *         callback fires exactly once; NULL `cb` is allowed (poll with
+ *         oakrender_ticket_wait()/oakrender_ticket_is_finished()).
+ */
+OakRenderTicket *oakrender_ticket_render_frame(
+	const oakrender_video_ticket_params *params,
+	oakrender_ticket_finished_fn cb, void *userdata);
+
+/**
+ * @brief Submit an audio render ticket (RenderManager::render_audio()).
+ *
+ * @param output_node Connected sample output node.
+ * @param params Audio params (borrowed oakcore handle).
+ */
+OakRenderTicket *oakrender_ticket_render_audio(
+	OakNodeNode *output_node, int64_t in_num, int64_t in_den,
+	int64_t out_num, int64_t out_den, const OakAudioParams *params,
+	int mode, oakrender_ticket_finished_fn cb, void *userdata);
+
+int oakrender_ticket_is_finished(OakRenderTicket *ticket);
+
+/** @brief Block until the ticket finishes. */
+int oakrender_ticket_wait(OakRenderTicket *ticket);
+
+int oakrender_ticket_cancel(OakRenderTicket *ticket);
+
+/** @brief OAKRENDER_TICKET_* or negative error. */
+int oakrender_ticket_get_type(OakRenderTicket *ticket);
+
+/** @brief Ticket timestamp (video tickets). */
+int oakrender_ticket_get_time(OakRenderTicket *ticket, int64_t *out_num,
+							  int64_t *out_den);
+
+/** @brief Ticket time range (audio tickets). */
+int oakrender_ticket_get_range(OakRenderTicket *ticket, int64_t *in_num,
+							   int64_t *in_den, int64_t *out_num,
+							   int64_t *out_den);
+
+/**
+ * @brief The resulting frame (video tickets). *out receives a retained
+ *        OakCodecFrame (release with oakrender_codec_frame_free()).
+ *        OAKRENDER_E_STATE when unfinished, OAKRENDER_E_FAILED when the
+ *        ticket has no frame result.
+ */
+int oakrender_ticket_get_frame(OakRenderTicket *ticket,
+							   OakCodecFrame **out);
+
+/**
+ * @brief The resulting samples (audio tickets). *out receives a copy
+ *        (release with oakcore_samplebuffer_free()).
+ */
+int oakrender_ticket_get_samples(OakRenderTicket *ticket,
+								 OakSampleBuffer **out);
+
+/** @brief Free the ticket handle (safe on finished tickets; cancels and
+ *        waits on running ones). No-op on NULL. */
+void oakrender_ticket_free(OakRenderTicket *ticket);
+
+/**
+ * @brief Toggle aggressive garbage collection on the render manager
+ *        (RenderManager::set_aggressive_garbage_collection()).
+ */
+int oakrender_manager_set_aggressive_gc(int enabled);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif //OAK_EDITOR_RENDER_TICKET_H

include/task/project.h

@@ -21,9 +21,12 @@
 #ifndef OAK_EDITOR_TASK_PROJECT_H
 #define OAK_EDITOR_TASK_PROJECT_H
 
+#include "codec/encoder.h"
+#include "node/colormanager.h"
 #include "node/footage.h"
 #include "node/node.h"
 #include "node/project.h"
+#include "node/sequence.h"
 #include "task/task.h"
 #include "undo/undocommand.h"
 
@@ -67,6 +70,15 @@ int oaktask_import_invalid_count(OakTaskTask *t);
 int oaktask_import_invalid_at(OakTaskTask *t, int index, char *buf,
 							  int buf_size);
 
+/** @brief olive::PreCacheTask. */
+OakTaskTask *oaktask_create_precache(OakNodeFootage *footage, int index,
+									 OakNodeSequence *sequence);
+
+/** @brief olive::ExportTask (params POD from codec/encoder.h). */
+OakTaskTask *oaktask_create_export(OakNodeNode *viewer,
+								   OakNodeColorManager *color_manager,
+								   const oakcodec_encoding_params *params);
+
 /**
  * @brief Image-sequence confirmation callback (facade/UI concern;
  *        olive::ProjectImportTask::set_image_sequence_confirm_callback).